2019, Vol.28, No.6

Journal of Environmental Impact Assessment 2023 KCI Impact Factor : 0.51

pISSN : 1225-7184
https://journal.kci.go.kr/kseia

The purpose of this study was to validate the EFDC model forthe weir pool of GangjeongGoryong Weir located in NakdongRiver, and evaluate the effect offlow control and phosphate loading reduction on the water quality and algae biomass by group (Diatom, Green, Cyanobacteria). As a result of model validation using 2018 experimental data,the time series of waterlevel and vertical distribution of water temperature, DO, organic matter, nitrogen, and phosphorus time series were properly simulated. Seasonal fluctuations of algae biomass by group were adequately reproduced, but the deviations between measured and simulated values were significant in some periods. As a result of scenario simulations to control the waterlevel and flow rate, the thermal stratification was resolved as the water level was lowered and the flow rate increased. The flow velocity at which the water temperature stratification was resolved was about 0.1 m/s, which is consistent with the previous study results of BaekjeWeirin Geum River. Simulations ofthe 2Q flow scenario showed that Chl-a decreased by 8.7% and the cell density of diatom and green algae declined. The cell density of cyanobacteria increased, however, because the high concentrations of cyanobacteria in the upstream boundary conditions directly affected downstream due to increased flow velocity. In the scenario simulation of reducing the influent phosphate load concentration (average 0.056 mg/L) to 50%, Chl-a decreased by 13.6%.The results suggestthatthe upstream algae concentration and phosphorus load reduction should be considered simultaneously with hydraulic control to prevent algal overgrowth of GangjeongGoryong Weir.

In this study, 49 major WCS(Wildlife Crossing Structure), including Baekdu-daegan, were evaluated for the effectiveness of WCS on using the daily average frequency index and diversity Index comparing the number of species that appear with the surrounding habitats. According to the analysis, the average use frequency of the entire WCS was 1.4 times, and the average number of WCS exceeded the average was 17 and 34.7 percent of the total. There were 18 WCS with the same number of habitats and species that appeared in the same area, or 36.7 percent of the total. The daily average use frequency and variety were all analyzed at 10 efficient WCS, accounting for 20.4 percent of the total. According to the results of an site survey on the compliance rate of 4 efficient WCS, the compliance rate of the Deoksanjae overpass was the best in location selection, specifications, vegetation cover and soil, fence. The results of this research will be used as basic data for the study of WCS effectiveness, including the improvement of functions of new and installed WCS.

In orderto quantify the effect of the newly established the Total Water Load Management System in Sapgyo watershed, this study predicted the achievement of the target water quality at each unit watershed and the water quality according to the flow section. The HSPF model, which is the watershed runoff model, was constructed and operated based on 2015, and the water quality was predicted by inputting the loads in finaltarget year(2030). The Load Duration Curve (LDC) was created using the simulated results of base year and target year. As a result of plotting water quality by flow conditions, it was simulated to be close to the BOD target with a difference of 0.1 ~ 0.2 mg/L in allthree watersheds during the mid-range flow interval (40 ~ 60%). In case of T-P, although the target water quality was not set, the water quality was improved by Cheonan A 46%, Kokgyo A 29% and Namwon A 25%. The Muhan and Sapgyo river basins meetthe target grade of middle-watershed standards. The improvement effect will be positive, as water quality, which achieves the target of Total Load Management System and the target grade of the middle-watershed standards will be expected to flow into the Sapgyo lake.